this might not be possible..........or maybe it is.
Often times on T-mobile 3g falls to EDGE. and this happens even in the heart of a 3G city like Chicago. With UMTS blanketing the city I dont know why the phone randomly goes to EDGE/GSM at times but what if there was an app to only use 1700/2100? I have see Euro phones that let you select modes between GSM and UMTS so maybe its possible in this case to keep the G1 on 3G when you are in an area where such a network is readily available.